1. Field of the Invention
The invention lies in the field of conveyor technology and relates to a gripper according to the preamble of the independent patent claim. The gripper is suitable for gripping and for the conveying of flat objects while they are held, in particular of printed products such as newspapers, magazines or brochures or of small groups thereof.
2. Description of Related Art
It is known to convey flat objects, in particular printed products such as newspapers, magazines or brochures, in compact conveyor flows, wherein the printed products are conveyed consecutively and aligned essentially parallel to one another, and the conveyor direction is aligned perpendicularly or obliquely (not parallel) to the main surfaces of the printed products. Thereby, the distances between the consecutive printed products is usually significantly smaller that the surface extension. Gripper transporters are applied for example for conveying such compact conveyor flows. These comprise a plurality of grippers which are fastened on a conveyor member, for example on a joint link chain, wherein the chain is revolvingly driven in a channel, and the grippers are designed for gripping a printed product, or a small group of printed products and conveying the product or the products while they are held.
The mentioned grippers usually comprise two clamping tongues, which may be pivoted relative to one another into an open and into a closed configuration with control/cam means arranged along the conveyor path, wherein clamping jaws which are aligned to one another and which are arranged at the distant ends of the clamping tongues, in the open configuration are distanced to one another and not capable of clamping, and in the closed configuration, these clamping jaws are pressed against one another or against a region of a printed product arranged therebetween. For gripping a printed product, a region of this is positioned between the clamping jaws of the open gripper and the gripper is then closed. For the held conveying, the gripper is held in the closed configuration, is advantageously locked in the closed configuration, and is opened or unlocked again for letting go of the printed product.
One example of such a gripper is described in the publication DE-3102242 (or U.S. Pat. No. 4,381,056). The gripper comprises two clamping tongues which are provided with clamping jaws which are aligned to one another. The first clamping jaw is firmly arranged on a gripper body and the second clamping jaw is pivotably arranged in the gripper body with the help of a shaft. The second gripper tongue at its proximal end comprises a spiral spring which is fastened on the shaft and winds around this. The spiral spring remains relaxed as long as the second clamping tongue, when the shaft is rotated relative to the gripper body, moves along with this, which means is accordingly pivoted. If however the clamping jaw of the second clamping tongue bears on the clamping jaw of the first clamping tongue and the shaft is rotated further, the spiral spring tensions and thereby transmits a clamping force onto a printed product clamped between the clamping jaws of the two clamping tongues. A cam lever with a cam roller engages on the shaft of the second clamping tongue for opening and closing the gripper and for chucking the second clamping tongue, and stationary cams are provided along the conveyor path, on which the cam roller rolls. Furthermore, the gripper comprises means with which the second clamping tongue or the shaft is locked in its closed and chucked position relative to the first clamping tongue. For this, in each case a locking element is arranged on the shaft and on the first clamping tongue. As soon as the shaft has reached a predefined rotation position, the locking elements lock into one another. The locking is opened by way of a pawl which is connected to the locking element on the first clamping tongue and which may be activated by a stationary control/cam element.
It is the object of the invention to improve a gripper of the type mentioned above, in particular the gripper according to DE-31202242 described briefly above, to the extent that these grippers may be applied for gripping and conveying a wide spectrum of flat objects. In particular, the grippers according to the invention should be suitable not only for securely gripping thicker and in particular heavier, and also very thin and light, flat objects, and securely conveying them in a held manner, but it should also be suitable for securely gripping flat objects and in particular also groups of flat objects which have regions of different thickness, and securely conveying them in a held manner. Moreover, the gripper according to the invention should also render it possible to grip the mentioned wide spectrum of flat objects in a clamping manner and in a manner such that forces between the clamping jaws of the clamping tongues and the gripped object, or between individual parts of the gripped object, and which act on the printed products in a rubbing and thus smearing manner, may be avoided to a such an extent, that one may also handle printed products on which the printed inks have not yet developed their final resistance to smearing.